Speed-control system for electric motors



Feb. 19,1929. 1,702,388 7 D. C LARSON ET AL,

SPEED CONTROL SYSTEM FOR'ELECTRIC uo'rons Filed March 25, 1923 Patented Feb. 19, 1929.

UNITED STATES 1,702,388 PATENT OFFICE.

DAVID C. LARSON, OF YONKERS, AND GEORGE W. LAUTRUP AND RAYMOND A. WAITE, O1 NEW YORK, N. Y., ASSIGNORS TO OTIS ELEVATOR COMPANY, OF JERSEY CITY, NEW JERSEY, A CORPORATION OF NEW JERSEY.

SPEED-CONTROL SYSTEM FOR ELECTRIC MOTORS.

Application filed March 23, 1923.

6 timing the operation of magnet switches is the use of mechanical dash pot or the like. All mechanical retarding means however are subject to wear and consequent loss of accuracy and it is therefore desirable to use an electric timing device.

It is well known that the time required to increase or decrease the current in an electric circuit may be controlled by the ratio of the inductance L to the resistance R and R is known as the time constant of the circuit.

To utilize this principle in the timing of magnet operated switches by so constructing the winding and core to give a practical time constant, involves the use of undesirably large switches.

We have found that a coil having the proper inductance and resistance may be used in series with the magnet coil of an ordinary commercial switch whereby any reasonable time of closing may be secured, due attention being paid to the design of the switch used. We have further found that a single inductance may be used in series with a plurality of magnet switches to give different time intervals for closing the various switches, by suitably choosing the air-gaps and coils of the switches and properly arranging the circuits. By the use of resistances of proper value shunted across the various switch coils and the common inductance, any reasonable time element may be provided for the opening of the various switches. Such an arrangement is advantageous in controlling the acceleration and retardation of elevator motors operating under any system of control, since it affords a means of closing and opening switches in accordance with a predetermined plan independently of the speed or voltage of the elevator motor. It is particularly advantageous in connection with the Ward Leonard system of speed control, in connection with which our invention will be fully described hereinafter.

The object of this invention is to provide an automatic means for accurately timing the operation of direct current magnet switches, both in closing and opening, by the use of an inductance with a relatively large time con- Serial' No. 627,032.

stant external to the magnet switch itself and connected inseries with the magnet coil, together with a resistance in parallel with the magnet coil or in parallel with both the inductance and the magnet coil.

In the Ward Leonard type of control, the speed of the elevator motor is regulated by varying the Voltage of the generator supplying power to the motor. This change in voltage is obtained by increasing or decreasing the field strength of the generator by varying the resistance in series with the shunt field winding of the generator. A timing device for regulating the operation of the magnet switches controlling the resistance in ser1es with generator field is desirable in order to obtain predetermined acceleration and retardation of the elevator.

The application of this invention described below, shows an electric timing device adapted to control such magnet switches.

The drawing shows a wiring diagram of a Ward Leonard control system for an elevator including the automatic timing device. Elevator car 1 is connected to driving sheave or drum 2 by ropes 3 over idler sheaves 4. The counterweight 5 is connected to driving sheave or drum 2 by ropes 6 over idler sheaves 7. Any well known method of roping may be used however. Driving sheave or drum 2 is connected to elevator motor M and brake BM is mounted to act upon motor and driving sheave shaft. Field M F is the shunt field of elevator motor M. The motor generator set consists of driving motor M and generator G. the latter supplying power to elevator motor M. Field MF is the shunt field of the motor M; field GF is the shunt field of the generator G and field GS is the series field of the generator G. Switch S is a main line knife switch for supplying power to motor M and switch S is a knife switch for supplying power to fields GF and MF and the controller magnets. Switch CS is the controller operating switch located in the car.

The controller consists of up and down magnet reversing switches A and B having main coils 8 and 9 and holding. coils 10 and 11 respectively. Magnet switches C, D, E

and F with coils 12, 13 14 and 15 respectively 7 are used to control the resistance R in series with the generator field GF and for identification may be called accelerating switches.

Inductance L is in series with accelerating switch coils. Its function will be described below. Resistance R is in parallel with generator field GF; resistance R is in parallel with inductance L and switch coils 13 and 14; resistance R is in parallel with inductance L and switch coil 12; resistance R is in parallel with coil 10 of switch A and resistance R is in parallel with coil 11 of switch B.

The operation of the controller is as follows: Assume that main line switches S and S are closed, thereby causing motor generator set to be in operation and shunt field M'F to be energized. Also assume that it is desired to run the car in the up direction. The handle of the car switch CS is moved toward the left. Segment 16 attached to car switch handle then bridges contacts 17, 18, 19, 20 and 21 in car switch. This completes the circuit for reversing switch coil A as follows:

minus supply line, switch S, wire 22, contact 18, car switch segment 16, contact 17, wire 23, coil 8 of switch A, wire 24, contact 25 on switch B, wires 26 and 27, switch S plus supply line. Coil 8 being energized, switch A operates making circuit for the brake magnet BM and generator field GF as follows: for the brake magnet, plus line, switch S wire 27, contact 28, plate 29, contact-30, wire 31, coil BM, wires 32'and 33, switch S minus line: for the generator field, plus line, switch S wire 27, contact 28, plate 29, contact 34, wire 35, generator shunt field GF and resistance R in parallel, wire 36, contact 37, plate 38, contact 39, wire 40, coil 10 and resistance R in parallel, wire 41, resistance R, wire 42, switch S minusline. The brake magnet will then lift, releasing the brake and motor will start provided of course the generator G gives-sufficient voltage with all of resistance R in series with its shunt field GF.

The movement of car switch handle to left also makes circuit for the coils of the various accelerating switches C, D, E and F, as follows: for coil 12 of switch G, minus line, switch S wire 22, car switch contact 18, segment 16, car switch contact 19, wire 43, coil 12, wires 44 and 45, inductance L, wire 46, switch S plus line. In parallel with coil 12 and inductance L is resistance R connected as follows: from wire 43, wire 47, resistance R wire 48, to wire 46. As the circuit for coil 12 of switch C is now complete, this switch will operate and close its contacts and short circuit the portion of resistance R between points 49 and 50 by way of wires 54 and 55, contact 56, wire 57. The closing wire 73, contact 58 on switch C, wire 59, coil 13 of switch D, wire 60, ,coil 14 of switch E, wire 45, inductance L, wire 46, switch, S plus line. In parallel with coil 14 ofswitch E in contact 61 connected from wire'60 to wire 45; also in parallel with coils '13, 14 and inductance L is resistance R connected from wire 59, wire 74, resistance R wire 48. The circuit for accelerating switches I) and. E is now complete. Switch D however will operate before switch E, due to breaking contact 61 mounted on switch D being connected in parallel with coil 14 on switch E. When this contact 61 is opened by the operation of switch D, coil 14 of switch E becomes energized and the latter switch will operate. The action of both switches D and -E is retarded by the effectof the time constant of the inductance L connected in series with these two coils.

The closing of accelerating switch D short circuits the portion of the resistance R between points 49 and 51 by way of wire 54, contact 62, wire 63, point 51.- The closing of switch E likewise short circuits the portion of the resistance R between points 49 and 52 by way of wires 54, 55, 64, contact 65, wire 66, to point 52.

The closing of switch E also completes the circuit for switch F as follows: minus line, switch S wire 22, car switch contact 18, segment 16, contact 21, wire 67, contact 68 on switch E, wire 69, coil 15, wire 45. inductance L, wire 46, switch S plus line. The ac'celerating switch F will now operate and short circuit the resistance R from 49 to 53 by way of wires 54, 55, 64, 70, contact 71. wire 72, to point 53. The action of switch F will also be retarded by the time constant of the inductance L in series with the coil of this switch.

tions of resistance R in series with generator.

field GF strengthens this field and consequently increases the voltage of the generator G supplying power to motor'M'. This change in voltage results in an acceleration of motor M until the desired full Speed is reached. During the acceleration, the coil 10 of switch A will have a constantly increasing voltage impressed upon it and at some point during the acceleration, this coil, 10, will become *sufiicently energized to hold switch A with its contacts closed independent of the operating coil 8.

The elevator car is now running at full speed in the up direction with switches A, C, D, E, and F on controller closed. Assume that it is desired to stop the car and in so doing the car switch CS is thrown to center or ofi position. The first circuit to be broken lltl is that of coil of switch F by the opening of contact 21 in car switch. Switch F will then open its contact 71 thereby inserting a portion of resistance in series with field GF. This will result in a reduction of voltage of generator G and a consequent reduction in speed of inotorM'. In a similar manner ac celerating switches E, D and G will open their contacts in the order stated.

The method of timing the opening of these various switches is a part of my invention, and consists of the inductance L in series with the-,accelerating switch coils and various values of resistance such as R and R connected in parallel in such a way as to produce a closed circuit around accelerating coils and inductance. With this arrangement the time constant of this inductance will regulate the time of opening of the various switches. The time constant of the inductance can be regulated by changing the inductance itself and by varying resistances It and R In stopping, the last car switch contact-to be broken is contact 17 in circuit of coil 8 of switch A. The opening of this contact 17 will however not cause switch A to open as this switch is held closed by coil 10. This coil will be deenergized in proportion to the change in resistance R, and also as a result of the time constant of the generator field GF in series with the coil 10. The resistance R in parallel with GF may be regulated to of the time constant of an external indnctance in series with the switches to be timed. The time constant of this inductance may be varied by changing the inductance itself and by the use of various resistances in parallel with the inductance alone or in parallel with both the inductance and the coil of the switch to be timed.

Having described the invention what is desired to be claimed and secured by Letters Patent of the United States is:

1. In a direct current control system, a plurality of switches, each switch having an operating coil and means for timing the opening and closing of said switches, said means comprising an inductance in series with said coils and a resistance in parallel with the inductance and said coils.

2. In a direct current control system, a plurality of switches, each switch having an operating coil, and means for timing the opening and closing of said switches, said means comprising an inductance in series with said coils and a plurality of resistances, one for each coil, each resistance being in parallel with its respective coil and said inductance. I

3. In a direct current control system for motors, the combination of a plurality of electro-magnet switches, the coils for certain ones.

of the switches being in series and the coils for certain others of the switches being in parallel with each other, an inductance in series with the coils of said switches, and resistance connected across said inductance and certain of the coils of said switches, whereby the operation of each of said switches is delayed upon energization of its coil and the operation of those switches havin resistance in parallel to their coils is delaye upon deenergization of their coils.

4. In a direct current control system, a resistance, a plurality of switches for short cir cuiting said resistance in steps, each switch having an operating coil and the coils for certain of said switches being in series and the coils for certain others of said switches being in parallel, an inductance in series with all of said coils, and resistance connected across said inductance and certain of said coils, whereby the operation of each of said switches is delayed upon energization of its coil and the 0 eration of those switches having resistance in parallel to their coils is delayed upon deenergization of their coils.

5. In combination; a motor; and means for controlling the acceleration and retardation of the motor, said means Comprising a resistance, a plurality of direct current switches for short-circuiting said resistance in steps, each switch having an operating coil, an inductance in series with said coils, and resistance connected across said inductance and certain of said coils, whereby the operation of each bf said swithces is delayed upon energizationof its coil and the operation of those switches having resistance in parallel to their coils is delayed upon deenergization of their coils.

6. A motor control system comprising the combination with a working motor, a generator for supplying power to said motor, a separately excited field winding for said generator, a. resistance in series with said field winding and adapted to be varied in steps; of a plurality of electro-magnetic switches for controlling said resistance and an inductance in series with the coils of all of said switches and resistance in parallel with said inductance and said coils for preventing the operation of said switches for a predetermined time after thel energization or deenergization of their 001 s.

7. In the Ward Leonard system of speed control for motors, the combination pf electro-magnetic reversing switches to control the field of the generator and direction of ro tation of the working motor, and electro-mag netic switches to control the acceleration and retardation of said motor, the coils for certain ones of said last mentioned switches being in series and the coils for certain others of said last mentioned switches being in parallel with each other, and holding coils for the reversing switches in series with the generator field winding for timing the opening of the reversing switches.

8. A motor control system comprising the combination with a working motor, a generator for supplying power to said motor, a. separately excited field winding for said genera- 

